The invention relates to an X-ray examination apparatus which includes an X-ray source and an X-ray detector.
A known X-ray examination apparatus is described in international application WO 00/75872. The known X-ray examination apparatus reconstructs a three-dimensional data set from the series of projection images. The projection images are acquired notably by irradiating the patient to be examined from the respective orientations while using an X-ray beam emitted by the X-ray source. The orientations at which the projection images are formed are accurately calibrated, thus enabling accurate three-dimensional reconstruction without excessive artifacts. A contrast medium is administered to the patient to be examined and the projection images are acquired when the blood vessels in the part of the anatomy to be examined are filled with contrast medium. The three-dimensional reconstruction produces a three-dimensional data set which associates data values with three-dimensional spatial positions. This data set represents the structure of the blood vessels at an instant at which the vessels are filled with the contrast medium. It has been found in practice that the diagnostic information provided by display of the three-dimensional data set is still inadequate.
The invention is arranged to form a series of projection images at respective orientations of the X-ray source and the X-ray detector relative to a predetermined frame of reference. The orientations being calibrated relative to the frame of reference, and reconstructing a basic three-dimensional data set from the series of projection images.
It is an object of the invention to provide an X-ray examination apparatus which enables the spatial image information of the three-dimensional reconstruction to be combined with image information other than that contained in the projection images used for the three-dimensional reconstruction.
This object is achieved by means of an X-ray examination apparatus in accordance with the invention in which the positions of the X-ray source and the X-ray detector relative to the frame of reference are calibrated for one or more additional directions of observation. As a result, image information available for the one or more additional observation directions can be reproduced in registration with the three-dimensional data set. The combined rendition of the three-dimensional data set and the image information associated with the one or more additional directions of observation faithfully represents the spatial aspects of the object to be examined which is represented by the projection images wherefrom the basic three-dimensional data set is reconstructed and by the image information associated with the additional direction (directions) of observation. These and other aspects of the invention will be elaborated hereinafter on the basis of the following embodiments of the invention which are defined in the dependent claims.
For example, the image information associated with the additional direction (directions) of observation is available in the form of one or more additional X-ray images. Preferably, such additional X-ray images are formed as shadow images, each of which has its own projection direction. The projection directions wherefrom the additional X-ray images are formed then constitute the additional direction (directions) of observation. The additional X-ray images and the three-dimensional basic data set are reproduced with the correct mutual relationship. For example, it is advantageous to form the series of projection images at a comparatively low energy and intensity of the X-rays and to acquire the additional X-ray images at a higher intensity and/or energy of the X-rays. The patient to be examined is thus exposed to a low X-ray dose for the acquisition of the projection images for the basic three-dimensional data set. The additional X-ray images have a low noise level and hence a high diagnostic quality. The X-ray examination apparatus in accordance with the invention enables the high diagnostic quality of the additional X-ray images to be combined with the spatial image information in the basic three-dimensional data set.
Moreover, it is also possible to reproduce, together with the basic three-dimensional data set, image information acquired before or after the projection images wherefrom the basic three-dimensional data set is reconstructed. Variations in time in the object to be examined can thus be faithfully and accurately reproduced with the spatial structure of the object. For example, favorable results are obtained for the reproduction of the process of the filling of a part of the vascular system of the patient to be examined with blood with contrast medium. Preferably, there is formed a succession of additional X-ray images which show successive phases of the filling of the vascular system with blood with contrast medium. The spatial structure of the vascular system is known from the basic three-dimensional data set and the additional X-ray images provide the dynamics of the flow of the blood through the vascular system. Because the projection directions of the additional X-ray images, that is, the additional directions of observation and the projection images for the three-dimensional data set have been calibrated relative to the same frame of reference, both types of information can be made to correspond accurately. Consequently, the dynamics of the flow of blood through the vascular system can be accurately visualized in space while a comparatively low X-ray dose suffices nevertheless.
Preferably, the basic three-dimensional data set is continuously updated on the basis of the additional X-ray images; for example, it is handy to perform an update whenever a new additional X-ray image becomes available. A dynamic series of three-dimensional data sets is thus formed, successive data sets in such a dynamic series then relate to successive phases of the filling of the blood vessels with blood with contrast medium.
Furthermore, it is advantageous to store a number of preferred additional directions of observation and/or the corresponding positions for the X-ray source and the X-ray detector in advance in a memory. This facilitates the positioning of the X-ray source and the X-ray detector for the acquisition of the additional X-ray images. When the user (users) himself (themselves) is (are) allowed to store a plurality of preferred additional directions of observation and/or the associated positions of the X-ray source and the X-ray detector, the personal preferences of the relevant user (users), for example, individual radiologists, can be taken into account.
Preferably, it is ensured that for the positioning of the X-ray source and the X-ray detector for the acquisition of the one or more additional X-ray images the X-ray source and the X-ray detector are moved from a predetermined starting position to the desired position. Consequently, the desired position for the acquisition of the additional X-ray images is always reached from the same direction. It has been found that the desired position is thus accurately reached, because inter alia mechanical hysteresis effects are avoided in particular.
The following description, claims and accompanying drawings set forth certain illustrative embodiments applying various principles of the present invention. It is to be appreciated that different embodiments applying principles of the invention may take form in various components, steps and arrangements of components and steps. These described embodiments being indicative of but a few of the various ways in which some or all of the principles of the invention may be employed in a method or apparatus. The drawings are only for the purpose of illustrating an embodiment of an apparatus and method applying principles of the present invention and are not to be construed as limiting the present invention.